bind1st 函式

為一 helper 樣板函式，此函式建立一個配接器，透過繫結二元函式第一個引數為指定值將二元函式物件轉換成一元函式物件。

template<class Operation, class Type> 
   binder1st <Operation> bind1st( 
      const Operation& _Func,  
      const Type& _Left 
   );

參數

• _Func
  要轉換的二元函式物件對一元的函式物件。

• _Left
  二元函式物件的第一個引數所繫結的值。

傳回值

一元的函式物件從繫結的結果二元函式物件的第一個引數傳遞給 _Left.的值

備註

函式繫結器是一種函式，配接器，因為會傳回函式物件，可以用來函式複合的某些型別建構更複雜且更強大的運算式。

如果 _Func 是 Operation 型別的物件，而且 c 是常數，則為 bind1st (_Func， c) 與 binder1st 類別建構函式 binder1st<Operation> (_Func)， c等於且更方便。

範例

// functional_bind1st.cpp
// compile with: /EHsc
#include <vector>
#include <functional>
#include <algorithm>
#include <iostream>

using namespace std;

// Creation of a user-defined function object
// that inherits from the unary_function base class
class greaterthan5: unary_function<int, bool>
{
public:
    result_type operator()(argument_type i)
    {
        return (result_type)(i > 5);
    }
};

int main()
{
    vector<int> v1;
    vector<int>::iterator Iter;

    int i;
    for (i = 0; i <= 5; i++)
    {
        v1.push_back(5 * i);
    }

    cout << "The vector v1 = ( " ;
    for (Iter = v1.begin(); Iter != v1.end(); Iter++)
        cout << *Iter << " ";
    cout << ")" << endl;

    // Count the number of integers > 10 in the vector
    vector<int>::iterator::difference_type result1a;
    result1a = count_if(v1.begin(), v1.end(), bind1st(less<int>(), 10));
    cout << "The number of elements in v1 greater than 10 is: "
         << result1a << "." << endl;

    // Compare: counting the number of integers > 5 in the vector
    // with a user defined function object
    vector<int>::iterator::difference_type result1b;
    result1b = count_if(v1.begin(), v1.end(), greaterthan5());
    cout << "The number of elements in v1 greater than 5 is: "
         << result1b << "." << endl;

    // Count the number of integers < 10 in the vector
    vector<int>::iterator::difference_type result2;
    result2 = count_if(v1.begin(), v1.end(), bind2nd(less<int>(), 10));
    cout << "The number of elements in v1 less than 10 is: "
         << result2 << "." << endl;
}

需求

標題: <functional>

命名空間: std

請參閱

參考

標準樣板程式庫